Arc rotation detector



Feb. 27, 1968 DE CORSO m1 3,371,141

ARC ROTATION DETECTOR Filed April 11, 1967 EEHAEDLSDED ALARM AND FlLTER CONTROt F IG.2.

FIG.3

WITNESSES INVENTORS Serofino M. De.Corso v and Lee A. Kilgore v ATTORNEY United States Patent M 3,371,141 ARC ROTATION DETECTOR Serafino M. DeCorso, Media, and Lee A. Kilgore, Export, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 11, 1967, Ser. No. 629,996 5 Claims. (Cl. 13-9) ABSTRACT OF THE DISCLOSURE An arc rotation detector for use on an electrode in an arc furnace is provided to prevent damage to the electrode resulting from stoppage of arc rotation, and resulting in having the intensely 'hot are spot remain in one position on the electrode, and includes a pickup coil placed within the electrode tip or other arcing surface forming means, and shielded leads from the pickup coil toan instrument located outside the electrode structure for giving an alarm or shutting olf the power to the electrode. A filter at the instrument may be provided to allow passage of signals having a frequency corresponding to the frequency of the alternating current which supplies the power to the arc. The coil is wound symmetrically in a manner whereby, as long as the high speed are rotat-ion, which may be of the order of 1000 cycles per second, persists, the field coil will behave as though it were subjected to a field of uniform current flow in a cylindrical conductor, that is, the electric field on the coil at the power frequency will be negligible. However, when are rotation stops the pickup coil will be subjected to a high electromagnetic field from the current filament through the electrode to the tip which supplies the arc. When are rotation stops the field Within the tip cylinder is no longer negligible near the region of the are spot and a strong 60 cycle or other power frequency signal will be produced.

Background of the invention The field of art to which the invention pertains is electrodes for use in arc furnaces of the type Where the .arc is caused to rotate at a high speed around the arcing surface of the electrode to prevent burnthrough by the hot are spot. A coil is disposed within the tip, the coil being wound in such a manner that when the arc is rotating no substantial signal is induced therein at the frequency of the power which supplies the arc current, but when the arc stops a substantial power frequency signal is inducedin the coil.

Description of the prior art A copending arc rotation detector application is Serial No. 564,341, filed July 11, 1966, by George Comenetz for Method and Apparatus for Monitoring Arc Rotation on an Electrode and assigned to the assignee of the instant invention.

Summary of the invention The invention includes a pickup coil disposed within the arc tip which is composed of non-magnetic material, the pickup coil being wound in such a way that when the arc is rotating normally no substantial signal is induced in the coil at the power frequency of the current which produces the arc, while if the arc stops a substantial power frequency signal is induced in the coil. This signal is fed to alarm and control apparatus for if desired shutting olf the current to the arc. Another embodiment of the invention uses three coils symmetrically disposed and wound in a similar manner with respect to signals induced therein by a rotating and non-rotating are.

3,371 ,141 Patented Feb. 27, 1968 Brief. description of the drawing t-ip are provided, each coil being wound in such a manner as to have a strong power frequency signal induced therein only while the arc is not rotating.

Description of the preferred embodiments In FIGURE'I the electrode is generally designated 10 and has an electrode tip forming in an arcing surface generally designated 11, the are being shown at 16. The electrode tip is seen to include an annular member 12 generally U-shaped in cross section, and the supporting and body portion of the electrode is seen to include more generally concentric cylinders of increasing diameters 21, 22, 23 and 24, forming therebetween two fluid flow passageways 25 and 26 for the flow of fluid to and from the electrode tip. The field coil is mounted and sustained from above in the housing, which is also mounted and sustained from above to form a fluid flow passageway 15 communicating with the aforementioned fluid passageways 25 and 26. Passageway 15 extends around the entire electrode tip and provides a space in which the arc rotation detector coil or coils of the invention may be located.

In FIG. 1, leads 30 symbolize means for connecting the electrode to one terminal of a source of potential and lead 31 symbolizes means for connecting the melt of the furnace, which is at least current carrying to some degree, to the other terminal of the source of potential difference which produces are 16.

In FIG. 2 there is shown a coil according to one embodiment of our invention which it is understood is composed of wire which is electrically insulated so as not to make the electrical contact with the arcing surface forming member 12. It will be understood that current filaments exist in the electrode tip 11, these current filaments bunching at the site of the are spot, and the current filaments rotating rapidly around the arcing surface forming means 12 as the arc rotates at a speed of, for example, 1000 cycles per second. The coil of FIG. 2 designated 35, and disposed within the space 15, so long as the high speed are rotation is maintained, will behave as though it were subjected to a field of uniform current how in a cylindrical conductor, that is, the electromagnetic effect of the cell at the power frequency, for example 60 cycles, will be negligible. However, if the rotation stops, the pickup coil will be subjected to a high electric field from the current filament. The coil as noted has approximately circumferentially symmetric geometry. When the arc stops rotation the field with-in the tip cylinder is no longer negligible near the region of the are spot, and a strong 60 cycle signal will be produced. The tip forming portion 12 is composed of non-magnetic material. Shielded leads 36, '37 extend up through the electrodes supporting structure, pass out through the electrode body to a filter which passes a 60 cycle or other power frequency signal and designated 39, and thence to an alarm and control device 41 which may if desired be connected to cut off the current that supplies the are 16.

Particular reference is made now to FIG. 3, an embodiment of our invention employing three coils generally designated 51, 52 and 53, coil 51 having shielded leads 54 and 55, coil 52 having shielded leads 56 and 57, and coil 53 having shielded leads 58 and 59.

In supplying a suitable signal to the alarm and control device 41, the coils 51,. 52 and 53 may be series connected or may be parallel' connected in a suitable network to supply a 60-cycle signal to the filter 39.

Our invention includes the use of two coils, as well as three, the two coils covering substantially the entire periphery of the electrode.

Filter 39 may be omitted if not needed.

It is to be understood that the drawings and the foregoing written description are illustrative only and are not to be interpreted in a limiting sense.

We claim as our invention:

1. In an electrode for use in an arc furnace having an annular arcing surface forming an electrode tip, generally U-shaped in cross section, and having a magnetic field coil disposed therein to rotate the arc, having a supporting structure at least a portion of which is metallic and which is connected to one terminal of the source of potential and electrically connected to the tip, the field coil being supported in a housing in the hollow tip with an annular passageway, U-shaped in cross section, for the flow of cooling fluid near the arcing surface, the supporting structure having fluid flow passageways extending the length thereof for bringing fluid to the tip and removing fluid which has passed through the tip, the improvement which comprises a coil disposed within the electrode tip in the passageway therein, the coil being electrically insulated from the tip, the coil being constructed of relatively thin wire which does not obstruct the flow of fluid through the U-shaped annular passageway around the entire electrode tip, the coil having no substantial power frequency signal induced therein While the arc is rotating at a high speed, the coil having a. substantial power frequency signal induced therein when the arc stops rotation and the are spot remains in one point on the electrode tip.

2. Apparatus according to claim 1 including an alarm and control device operatively connected to receive the output on the coil.

3. Apparatus according to claim 2 including a filter interposed between the coil and the alarm and control device, the filter being constructed and arranged to pass the signal of power frequency.

4. Apparatus according to claim 1 including two additional coils within the tip, both supplying signals which are used jointly by the alarm and control device.

5. Apparatus according to claim 1 including one additional coil disposed within the tip, signals at both of the coils being used by the alarm and control device.

References Cited UNITED STATES PATENTS 501,825 7/1893 Coflin 13-9 975,794 11/1910 Potter 13-26 2,286,210 6/1942 Klemperer et al. 2l997 2,286,211 6/1942 Dawson et al. 2l9-97 2,472,851 6/1949 LandiS et a1. 315347 3,194,941 7/1965 Baird 219-121 BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

